Formation layers, lithological boundaries, sedimentary bedding, etc. in the underground can be defined through the interfaces between different lithologies, which produce seismic reflections due to impedance contrasts. These seismic reflections are referred to as seismic horizons, and interpretation of seismic horizons plays an important role in the structural characterization of 3D seismic data. Seismic horizons are commonly interpreted as being located along minimum, maximum, or zero crossing values in a seismic volume, and interpretations can be obtained by manual or automatic extraction of such surfaces. Structurally complex regions are a challenge to existing interpretation procedures, both automated and manual. For the manual interpreter, structural complexity produces ambiguities, and the interpretation process can become very time consuming. The continuity constraint incorporated by most automated algorithms may fail to hold. In particular, automatic continuation of an interpretation across faults is a challenge.
The present invention addresses this problem by laterally detecting and combining horizon segments having similar seismic waveforms. The mapping is not restricted to spatial continuity in the position of the seismic horizon, but instead determines possible lateral continuations based on similarity of signal shape. The inventive method represents waveforms as coefficients, typically seismic derivatives, that can be used to reconstruct the seismic trace in the vicinity of the extrema positions, such as by utilizing Taylor series expansions. The term “extrema” as used throughout this patent application includes any characteristics of seismic traces that can be used to track the positions of seismic horizons, such as minimum values, maximum values, zero-crossing values, midpoints between zero-crossing values and maximum or minimum values, etc. Derivatives that can be used in the Taylor series reconstruction and sub-sample accuracy extrema positions can be calculated based on orthogonal polynomial spectral decompositions of the seismic traces, such as described in U.S. Pat. No. 6,240,370, issued May 29, 2001 to Lars Sønneland et al.
The lateral continuations of horizons can be exploited to automatically estimate fault displacement, with a spatially varying displacement offset along the fault plane. Fault displacement influences the connectivity of hydrocarbon bearing lithologies, and assessment of the displacement provides an improved description of a reservoir. The present invention can calculate the displacement along pre-interpreted fault planes, for example fault planes that have been extracted from the seismic data using the methodology described in U.K. patent GB 2,375,448 B issued Oct. 15, 2003 to Schlumberger Holdings Limited.
Accordingly, it is an object of the present invention to provide an improved method of processing and interpreting seismic data. In one embodiment, this involves extracting surface primitives, and grouping extrema positions where these surface primitives are both spatially continuous along the extrema of the seismic volume and are continuous in class index in the classification volume.